From 144479ad7b4287bee4067f95e4218f614798a865 Mon Sep 17 00:00:00 2001
From: Stephan Hartmann <stha09@googlemail.com>
Date: Sun, 16 Jan 2022 19:15:26 +0000
Subject: [PATCH] sql: make VirtualCursor standard layout type

sql::recover::VirtualCursor needs to be a standard layout type, but
has members of type std::unique_ptr. However, std::unique_ptr is not
guaranteed to be standard layout. Compiling with clang combined with
gcc-11 libstdc++ fails because of this.

Bug: 1189788
Change-Id: Ia6dc388cc5ef1c0f2afc75f8ca45b9f12687ca9c
---
 sql/recover_module/btree.cc  | 18 ++++++++++++------
 sql/recover_module/btree.h   | 21 +++++++++++++++------
 sql/recover_module/cursor.cc | 24 ++++++++++++------------
 sql/recover_module/cursor.h  |  2 +-
 sql/recover_module/pager.cc  |  5 ++---
 sql/recover_module/pager.h   |  6 +++---
 6 files changed, 45 insertions(+), 31 deletions(-)

diff --git a/sql/recover_module/btree.cc b/sql/recover_module/btree.cc
index cc9420e5c05..f12d8fa32a2 100644
--- a/sql/recover_module/btree.cc
+++ b/sql/recover_module/btree.cc
@@ -136,16 +136,22 @@ static_assert(std::is_trivially_destructible<LeafPageDecoder>::value,
               "Move the destructor to the .cc file if it's non-trival");
 #endif  // !DCHECK_IS_ON()
 
-LeafPageDecoder::LeafPageDecoder(DatabasePageReader* db_reader) noexcept
-    : page_id_(db_reader->page_id()),
-      db_reader_(db_reader),
-      cell_count_(ComputeCellCount(db_reader)),
-      next_read_index_(0),
-      last_record_size_(0) {
+LeafPageDecoder::LeafPageDecoder() noexcept = default;
+
+void LeafPageDecoder::Initialize(DatabasePageReader* db_reader) {
+  page_id_ = db_reader->page_id();
+  db_reader_ = db_reader;
+  cell_count_ = ComputeCellCount(db_reader);
+  next_read_index_ = 0;
+  last_record_size_ = 0;
   DCHECK(IsOnValidPage(db_reader));
   DCHECK(DatabasePageReader::IsValidPageId(page_id_));
 }
 
+void LeafPageDecoder::Reset() {
+  db_reader_ = nullptr;
+}
+
 bool LeafPageDecoder::TryAdvance() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   DCHECK(CanAdvance());
diff --git a/sql/recover_module/btree.h b/sql/recover_module/btree.h
index eaa087a5c52..df0e0c937c0 100644
--- a/sql/recover_module/btree.h
+++ b/sql/recover_module/btree.h
@@ -101,9 +101,7 @@ class LeafPageDecoder {
  public:
   // Creates a decoder for a DatabasePageReader's last read page.
   //
-  // |db_reader| must have been used to read an inner page of a table B-tree.
-  // |db_reader| must outlive this instance.
-  explicit LeafPageDecoder(DatabasePageReader* db_reader) noexcept;
+  LeafPageDecoder() noexcept;
   ~LeafPageDecoder() noexcept = default;
 
   LeafPageDecoder(const LeafPageDecoder&) = delete;
@@ -151,6 +149,17 @@ class LeafPageDecoder {
   // read as long as CanAdvance() returns true.
   bool TryAdvance();
 
+  // Initialize with DatabasePageReader
+  // |db_reader| must have been used to read an inner page of a table B-tree.
+  // |db_reader| must outlive this instance.
+  void Initialize(DatabasePageReader* db_reader);
+
+  // Reset internal DatabasePageReader
+  void Reset();
+
+  // True if DatabasePageReader is valid
+  bool IsValid() { return (db_reader_ != nullptr); }
+
   // True if the given reader may point to an inner page in a table B-tree.
   //
   // The last ReadPage() call on |db_reader| must have succeeded.
@@ -164,14 +173,14 @@ class LeafPageDecoder {
   static int ComputeCellCount(DatabasePageReader* db_reader);
 
   // The number of the B-tree page this reader is reading.
-  const int64_t page_id_;
+  int64_t page_id_;
   // Used to read the tree page.
   //
   // Raw pointer usage is acceptable because this instance's owner is expected
   // to ensure that the DatabasePageReader outlives this.
-  DatabasePageReader* const db_reader_;
+  DatabasePageReader* db_reader_;
   // Caches the ComputeCellCount() value for this reader's page.
-  const int cell_count_ = ComputeCellCount(db_reader_);
+  int cell_count_;
 
   // The reader's cursor state.
   //
diff --git a/sql/recover_module/cursor.cc b/sql/recover_module/cursor.cc
index 4f827edf1b4..240de4999fe 100644
--- a/sql/recover_module/cursor.cc
+++ b/sql/recover_module/cursor.cc
@@ -28,7 +28,7 @@ VirtualCursor::~VirtualCursor() {
 int VirtualCursor::First() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   inner_decoders_.clear();
-  leaf_decoder_ = nullptr;
+  leaf_decoder_.Reset();
 
   AppendPageDecoder(table_->root_page_id());
   return Next();
@@ -38,18 +38,18 @@ int VirtualCursor::Next() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   record_reader_.Reset();
 
-  while (!inner_decoders_.empty() || leaf_decoder_.get()) {
-    if (leaf_decoder_.get()) {
-      if (!leaf_decoder_->CanAdvance()) {
+  while (!inner_decoders_.empty() || leaf_decoder_.IsValid()) {
+    if (leaf_decoder_.IsValid()) {
+      if (!leaf_decoder_.CanAdvance()) {
         // The leaf has been exhausted. Remove it from the DFS stack.
-        leaf_decoder_ = nullptr;
+        leaf_decoder_.Reset();
         continue;
       }
-      if (!leaf_decoder_->TryAdvance())
+      if (!leaf_decoder_.TryAdvance())
         continue;
 
-      if (!payload_reader_.Initialize(leaf_decoder_->last_record_size(),
-                                      leaf_decoder_->last_record_offset())) {
+      if (!payload_reader_.Initialize(leaf_decoder_.last_record_size(),
+                                      leaf_decoder_.last_record_offset())) {
         continue;
       }
       if (!record_reader_.Initialize())
@@ -101,13 +101,13 @@ int VirtualCursor::ReadColumn(int column_index,
 int64_t VirtualCursor::RowId() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   DCHECK(record_reader_.IsInitialized());
-  DCHECK(leaf_decoder_.get());
-  return leaf_decoder_->last_record_rowid();
+  DCHECK(leaf_decoder_.IsValid());
+  return leaf_decoder_.last_record_rowid();
 }
 
 void VirtualCursor::AppendPageDecoder(int page_id) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
-  DCHECK(leaf_decoder_.get() == nullptr)
+  DCHECK(!leaf_decoder_.IsValid())
       << __func__
       << " must only be called when the current path has no leaf decoder";
 
@@ -115,7 +115,7 @@ void VirtualCursor::AppendPageDecoder(int page_id) {
     return;
 
   if (LeafPageDecoder::IsOnValidPage(&db_reader_)) {
-    leaf_decoder_ = std::make_unique<LeafPageDecoder>(&db_reader_);
+    leaf_decoder_.Initialize(&db_reader_);
     return;
   }
 
diff --git a/sql/recover_module/cursor.h b/sql/recover_module/cursor.h
index 845b7852648..cc4e85f83f9 100644
--- a/sql/recover_module/cursor.h
+++ b/sql/recover_module/cursor.h
@@ -130,7 +130,7 @@ class VirtualCursor {
   std::vector<std::unique_ptr<InnerPageDecoder>> inner_decoders_;
 
   // Decodes the leaf page containing records.
-  std::unique_ptr<LeafPageDecoder> leaf_decoder_;
+  LeafPageDecoder leaf_decoder_;
 
   SEQUENCE_CHECKER(sequence_checker_);
 };
diff --git a/sql/recover_module/pager.cc b/sql/recover_module/pager.cc
index 58e75de2704..69d98cef98d 100644
--- a/sql/recover_module/pager.cc
+++ b/sql/recover_module/pager.cc
@@ -23,8 +23,7 @@ static_assert(DatabasePageReader::kMaxPageId <= std::numeric_limits<int>::max(),
               "ints are not appropriate for representing page IDs");
 
 DatabasePageReader::DatabasePageReader(VirtualTable* table)
-    : page_data_(std::make_unique<uint8_t[]>(table->page_size())),
-      table_(table) {
+    : page_data_(table->page_size()), table_(table) {
   DCHECK(table != nullptr);
   DCHECK(IsValidPageSize(table->page_size()));
 }
@@ -58,7 +57,7 @@ int DatabasePageReader::ReadPage(int page_id) {
                 "The |read_offset| computation above may overflow");
 
   int sqlite_status =
-      RawRead(sqlite_file, read_size, read_offset, page_data_.get());
+      RawRead(sqlite_file, read_size, read_offset, page_data_.data());
 
   // |page_id_| needs to be set to kInvalidPageId if the read failed.
   // Otherwise, future ReadPage() calls with the previous |page_id_| value
diff --git a/sql/recover_module/pager.h b/sql/recover_module/pager.h
index 07cac3cb989..d08f0932fab 100644
--- a/sql/recover_module/pager.h
+++ b/sql/recover_module/pager.h
@@ -6,8 +6,8 @@
 #define SQL_RECOVER_MODULE_PAGER_H_
 
 #include <cstdint>
-#include <memory>
 #include <ostream>
+#include <vector>
 
 #include "base/check_op.h"
 #include "base/memory/raw_ptr.h"
@@ -72,7 +72,7 @@ class DatabasePageReader {
     DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
     DCHECK_NE(page_id_, kInvalidPageId)
         << "Successful ReadPage() required before accessing pager state";
-    return page_data_.get();
+    return page_data_.data();
   }
 
   // The number of bytes in the page read by the last ReadPage() call.
@@ -139,7 +139,7 @@ class DatabasePageReader {
   int page_id_ = kInvalidPageId;
   // Stores the bytes of the last page successfully read by ReadPage().
   // The content is undefined if the last call to ReadPage() did not succeed.
-  const std::unique_ptr<uint8_t[]> page_data_;
+  std::vector<uint8_t> page_data_;
   // Raw pointer usage is acceptable because this instance's owner is expected
   // to ensure that the VirtualTable outlives this.
   const raw_ptr<VirtualTable> table_;
